Because of their unique properties, epoxy resins increasingly find a great variety of uses in the building industry (cf., for example, H. Saechtling, "Bauen mit Kunststoffen" [Building with Synthetic Resins], Carl-Hanser Publishers, Munich, 1973). In addition to the pure epoxy resin mortars utilized, for example, for coatings and adhesive bridges, interesting possibilities of application in the building industry are also offered by epoxy resin-cement mortars due to their good adhesive strength, satisfactory shrinkage characterics, and water retention capacity.
An essential prerequisite for the processing of epoxy resins is that the resin and the curing agent must react, under the weathering conditions prevailing at the building site, extensively completely with each other within an adequate period of time.
The binder mixture described in DOS No. 2,840,874, consisting of a hydraulic binder, an epoxy resin, the adduct from a polyamine and an epoxy compound, water, and optionally reactive diluents, pigments, and other auxiliary agents, is particularly suitable for renovating damaged reinforced concrete parts, since the use of a corrosion-protective primer is not necessary with this mixture.
A disadvantage of this bicomponent system is that, due to its limited stability, it must be prepared at the building site and processed within a relatively brief time span (about one-half hour). It is known that the ratio of curing agent to epoxy resin is of decisive importance. Therefore, the cited process wherein a rapid and very careful intermixing is important, lest impairment of quality occur, has received drawbacks under practical conditions.
According to U.S. Pat. No. 3,926,886, it is more advantageous to start with an epoxy resin-diammonium acetate or formate emulsion consisting of a liquid epoxy resin, water, and a substituted diammonium salt, and to effect curing in the presence of cement.
The diammonium salt has a dual function in this process: on the one hand, it is to liberate the basic diamine after reacting with the alkaline-acting cement, the diamine then curing the epoxy resin; on the other hand, it is to function as an emulsifier. However, stability of the thus-produced emulsion is not ensured, especially if the process must be carried out under extreme weather conditions. For this reason, even U.S. Pat. No. 3,926,886 suggests the addition to the mixture of up to 15% of a commercially available emulsifier. Yet, even after making such additions, the stability of the emulsion remains a critical factor.
It is further unsatisfactory that only certain diamines, containing ether groups, of the formula EQU R.sub.1 --O--R.sub.2 --NH--R.sub.3 --NH.sub.2
are suitable as the amine component. R.sub.1 is alkyl of at least 8 carbon atoms and R.sub.2 and R.sub.3 are lower alkylene of 2-4 carbon atoms.
In contrast, it is desirable to use more readily accessible polyamines and their condensation products for the preparation of emulsions. Polyamines, such as, for example, diethylenetriamine are, however, miscible with water in any desired ratio--in contrast to the diamines of U.S. Pat. No. 3,926,886. The formates and acetates of such polyamines cannot be emulsified with the customary emulsifiers, such as, for example, fatty alcohol oxethylates, alkyl sulfonates, or phosphoric acid half esters. On the other hand, only homogeneous, stable emulsions are capable of ensuring, in uniform quality, cold curing of the liquid epoxy compounds utilized.